1. Field of Invention
The present general inventive concept relates to components for batteries and more particularly to sintered anodes for lithium batteries and to methods and processes to fabricate such anodes.
2. Description of the Related Art
A secondary battery differs from a primary battery in that unlike a primary battery which is a single use non-rechargeable device, a secondary battery can be recharged many times. It value is established by a number of factors, for instance its power factors and cost, and of course its ability to be recycled quickly and reliably with steady power is a main factor in its value.
Lithium ion secondary batteries are today limited by the low function of current electrodes, particularly the anode. Lithium can function at levels as high as 3840 mAh/g, so the output of a secondary lithium ion battery is limited to less than this level by the level of the electrode materials, particularly the negative electrode. To date, graphite has been the material of choice since it can be structured for long life with many cycles of charge and discharge. This is currently more highly valued than level of power. So the capacity and number of cycles without unacceptable degradation of the lithium ion secondary battery mainly depends on an active material of an electrode, being the anode. The theoretical capacity of graphite is 372 mAh/g. It is engineered today with a capacity of as high as 350 mAh/g, with thousands of charge/discharge cycles.
In order to realize higher capacity secondary lithium ion batteries, it is necessary to supply a negative electrode material having a theoretical capacity closer to that of lithium. When the secondary lithium ion battery charges, lithium ions migrate from the cathode to the anode. This causes the anode to swell in acquiring this charge through the lithium ions. When the secondary lithium ion battery discharges lithium ions migrate from the anode to the cathode and this causes the anode to shrink. In the case of silicon, which provides a theoretical 4200 mAh/gram, this swelling and shrinking can be as much as 400%. Supplying a negative electrode, the anode, that can provide a capacity closer to lithium must be accompanied by an ability to provide service through many thousands of cycles with minimal degradation meaning this shrinking and swelling does not cause material damage that reduces or eliminates electrical conductivity in the structure.
U.S. Pat. No. 9,054,373, issued Jun. 9, 2015 to Abouimrane et al., teaches the fabrication of composite materials of a metal oxide and a metal carbon alloy to buffer the volume expansion associated with lithium alloying of metal oxides. In particular, Abouimrane et al. teach the mixing of tin cobalt carbon alloys with a metal oxide material. Ali Abouimrane and Khalil Amine disclose that “a small amount of silicon” can increase the capacity of an anode, but they teach that the amount of silicon that may be added is limited due to what they see as “large volume expansion and poor cycleability” associated with silicon. They teach that silicon oxides “can crack easily due to volume changes during charging and discharging cycles.”
Julius M. Schoop, in his doctoral dissertation, discusses the surface properties of porous tungsten, particularly in its use in dispenser cathodes. Schoop, Julius M., “Engineered Surface Properties of Porous Tungsten from Cryogenic Machining” (2015), Theses and Dissertations—Chemical and Materials Engineering, Paper 49 (Univ. of Kentucky). Schoop discloses porous tungsten that “operates much like a sponge that both holds and releases a secondary medium as needed.” Schoop in particular teaches porous tungsten backfilled with barium-based compounds.
Cronin, in his discussion of dispenser cathodes, discusses the possibility of dispenser cathodes “of the mixed-metal matrix type,” and in particular cathodes that combine either tungsten or molybdenum with one of the platinum family of metals. These cathodes are fabricated with “a controlled porosity matrix configuration impregnated with a barium calcium aluminate type mix.” Cronin, J. L., “Modern Dispenser Cathodes,” IEE Proc. 128(1) (February 1981).
Neither Schoop nor Cronin discuss porous tungsten in connection with anodes.
Kuzubov et al. discuss the lithiation of “graphitelike” [sic] boron carbide. Kuzubov, A. A., Fedorov, A. S., Eliseeva, N. S., Tomilin, F. N., Avramov, P. V., Fedorov, D. G., “High Capacity Electrode Material BC3 for Lithium Batteries Proposed by ab Initio Simulations,” Physical Review B 85 (2012), 195415.
Zhao et al. discuss composite anodes of graphene and silicon; in particular, they look at anodes developed by encapsulating silicon particles “via in-situ polymerization and carbonization of phloroglucinol-formaldehyde gel, followed by incorporation of graphene nanoplatelets.” Zhao, X., Li, M., Chang, K.-H., Lin, Y.-M., “Composites of Graphene and Encapsulated Silicon for Practically Viable High-Performance Lithium-Ion Batteries.”
Yi Cui and colleagues discuss alloying anodes “such as silicon” for high energy density lithium-ion batteries. Because these alloying anodes “usually exhibit a short cycle life due to the extreme volumetric and structural changes that occur during lithium insertion/extraction,” Cui et al. look at silicon nanostructures “that can accommodate the lithiation-induced strain.” McDowell, M. T., Lee, S. W., Nix, W. D., Cui, Y., “25th Anniversary Article: Understanding the Lithiation of Silicon and Other Alloying Anodes for Lithium-Ion Batteries,” Advanced Materials (2013) (Review Article), DOI: 10.1002/adma.201301795.